Thermoelectric pyrometer



May 18 1926.

H. S. MARSH ET AL THERMOELECTRIC PYROMETER Filed Sept. 24 1925 PatentedMay is, 192e.

HENRY S. MARSH AND RAL'F S. COCHRAN, 0F YOUNGSTOWN, OHIO.

THERMOELECTRIC P YROMETER.

Application filed September 24, 1925. Serial No. 58,384.

Our invention relates to the structure of thermo-electric pyrometer's,and consists in features of structures which render such instrumentsmore durable under service conditions.

kA theremo-electric pyrometer of our invention is shown somewhatdiagrammatically and in longitudinal'section in Fig. I of theaccompanying drawings. Fig. ll is a view in vertical section and Fig.III in horizontal section through an annealing furnace for steel sheetsand they show the pyrometer of our invention in one typical application.Figs. 1I and III are drawn to much smaller scale than Fig. l.

The pyrometer of our invention involves the use of a thermo-couple, thatis to say, two lengths of dissimilar metals united at one end andotherwise insulated one from the other. A circuit includingafgalvanometer or other measuring instrument is completed between theotherwise free ends of the two lengths of metal, and the united ends aresubjected to the temperature condition, whose value is to be determined.

The Leeds and Northrup potentiometer system includes a thern'io-coupleWhose component-s are vformed of base metals. Two wires are employed,one of iron, the other of constantan. Constantan is an alloy of copperand nickel. lVe preferably employ like materials, and our invention liesin structure.

For the particular use to be indicated below we take an eighth-inchconstantan wire eighteen feet long, indicated at 1, Fig. I. Upon thiswire we string a succession of clay beads 2, to serve as insulators.These beads are of suitable diameter to slip Within a three-eighths inchpipe, and may be an inch long. "Instead of an iron wire (the Leedsand-Northrup system employs iron).We provide a steel pipe 3 ofthree-eighths inch diameter and seventeen feet long. Into it we draw thebeaded constantan wire. The end of the -wire projects somewhat beyondthe final bead. The end ofthe pipe is hammered 'lat upon the end of theend of the included constantan wire, and the two metal bodies are weldedat this point 4, to

form the hot end of the thermo-couple.` Brass electrical couplings 5 and6 are at tached, one to the free end of the constantan wire 1, the otherto the free end of the steel pipe 3. Leads of constantan and of ironWire may manifestly be secured to these couplings, to complete a circuitthrough a galvanometer or other measuring instrument.

Turning to Figs. II and HI, 10 indicates thewall and 1l a ydoor of anannealing furnace. 12 is an annealing box Within the furnace, and 18 apile of sheets Within the annealing box. At about one third of thedistance from the base a layer 14 of one-inch bars is introduced in thepile, and between the bars of this layer the hot end of the pyrometer isintroduced. The pyrometer is proportioned and shaped to occupy theposition clearly illustrated in Figs. II and Ill. From the hot endwhich, as has been said, extends into the interior of the pile 13, thepyronieter extends externally of the pile to the base of the box; thencebeneath the rim and through the luting Which seals the box upon itsbase; thence across the furnace space, and out beneath the furnace door,and through the luting, if any, found at that point. The free ends ofthe couple, externally of the furnace, are connected as has been said.

It is that portion of the couple particularly which extends from beneaththe annealing box, across the furnace chamber to exit beneath thefurnace door which particularly is subject to destruction. The hotfurnace gases which at this point sweep over the introduced instrumenttend to destroy it rapidly.

By forming our couple as a wire within a tube, we protect one element ofthe couple by the other, and, as we have explained, We make the morecostly and more perishable member the inner member. We also have aconstruction in which one envelope of insulation suffices; otherwise,two are necessary, one surrounding each element of the couple.

Additionally, we provide an extra heavy, three-quarter inch steel sleeve7 and surround With it so much of the couple as in service extendsthrough the furnace space. When the couple has been formed and thesleeve 7 has been brought to place, the assembly is bent hot to theshape required for service. The assembly of the one-eighth inchconstantan Wire within the three-eighths inch steel ipe, may be bent byhand; accordingly eyond the sleeve 7 and toward its inner or hot end,the couple is easily shaped, to itboxes of different sizes.

But for our invention, such a. pyrometer made of wires and wrapped forprotection .with asbestos, is :de endable forl accuracy for only oneheat; uilt according to our invention, thev pyrometer lasts perfectlyfromv twenty to forty heats. We have found that so far as temperaturedetection is con- We have Aillustrated and particularly described oneapplication of the pyrometer of our invention; manifestly it isapplicable generally, and particularly Where the temperature of anobject is to be measured,

which is situated within a box or under a cover, and to 'which there isno approach but yacross a zone of oxidizing flame; to`carbon- 1z1ngboxes, for example.

Wewclaim as our invention:`

1. thermo-couple in which beads of insulation are strung upon one memberWhile the other member in tubular form envelops the assembly.

- 2. A thermo-couple of which one member in the form of a steel tubeencircles the otherl member in the form of -a Wire of dissimilar metal,a succession of clay beads being threaded on the wire Within the tube.,

In testimony' whereof we have hereunto set our hands. v

HENRY s. MARSH. HALF s. COCHRAN.

